The invention is directed to an apparatus for holding plate shaped electrical thin layer resistances which consist of or consist essentially of a thin metal layer on an electrically insulating carrier, especially for use in hot film anemometers for measuring flow velocity.
Heated thin layer resistances are frequently employed as components of hot film anemometers for measuring the flow velocity of gases and liquids, especially the intake air of internal combustion engines. The holding device for the heated thin layer resistance thereby must satisfy various requirements. On the one hand, the heating of the holder should be as small as possible in order to guarantee that the holder does not contribute to the withdrawal of heat to the fluid, and through this influence increase the response time of the anemometer with sudden change of the flow velocity. On the other hand, the thermal equilibrium between thin layer resistance and holder should be reached as quickly as possible in putting the anemometer into operation. Furthermore, there must be given an exact positioning of the film resistance relative to the flow direction, and the flowing around the thin layer resistance should be influenced as little as possible by the holding device.
There are known various methods to join thin layer resistances laminarly with a carrier body, e.g., by adhesives or solders. However, through this the heat capacity of the carrier body is thermally attached to the thin layer resistance so that the dynamic behavior is greatly damaged.
It is also known to produce the attachment of a thin layer resistance only via the electrical pigtails, which e.g., are welded or bonded to the metal resistance layer. There cannot be produced an exact and certain positioning of the thin layer resistance by this means.
Furthermore, there are known mechanical clamps which are suited for the electrical contacting of thin layer resistances and which also can serve as mechanical holder. These clamps, however, exhibit relatively large contact surfaces with the thin layer resistance so that the thermal equilibrium cannot be reached sufficiently quickly. Besides, an exact and certain positioning is only attainable at very high expense.
Therefore, it was the problem of the invention to develop a device for holding plate shaped electrical thin layer resistances which consist of or consist essentially of a thin metal layer on an electrically insulating carrier, especially for use in hot film anemometers for measuring flow velocities which makes possible an exact and certain positioning, guarantees a very quick establishment of the thermal equilibrium, and only immaterially influences the amount of heat drawn off from the heated thin layer resistance by the flow of fluid.